1. Field of the Invention
The present invention relates to a monitor device for use with an endoscope apparatus, which enables the operator of the endoscope apparatus to observe any image of an object, formed by an imaging device inserted in body cavities or ducts.
2. Description of the Related Art
In the field of medicine and the field of non-destruction inspection, endoscope apparatuses are usually used, each with a thin, long insertion section inserted into the body cavity or a duct, to monitor the image of an object existing in the body cavity or duct.
An endoscope apparatus of this type comprises an endoscope main unit, a light source device, a light guide cable, an imaging unit, a video processor, a signal cable, and a monitor device. The endoscope main unit has an insertion section that can be inserted into a body cavity or a duct. The light source device is provided outside the endoscope main unit and configured to apply light into the endoscope main unit. The light guide cable couples the light source unit to the endoscope main unit and can guide illumination light to the distal end of the endoscope main unit. The imaging unit is removably incorporated in the endoscope main unit and configured to photograph an object and generate an image signal representing the image of the object. The video processor converts the image signal generated in the endoscope main unit to an image signal representing an image that the monitor device can display. The signal cable can transmit the image signal to the video processor. The monitor device displays the image represented by the image signal.
Since the endoscope main unit is connected to the external devices by the light guide cable and the signal cable, its motion is limited by the length of these cables. Further, the operability of the endoscope main unit is somewhat limited by the weight and position of the cables.
In view of this, a new type of endoscope apparatus has been proposed. Jpn. Pat. Appln. KOKAI Publication No. 60-48011, for example, discloses an endoscope apparatus that incorporates an illumination device provided in the distal end and using light-emitting diodes (LEDs) as light source. This endoscope apparatus has no light guide cable, unlike the conventional apparatus that has a light guide cable extending from the proximal end of the endoscope main unit.
Electronic circuits have been miniaturized, thanks to the progress of one-chip fabrication and ultra-large-scale integration. At present, an endoscope apparatus is proposed, whose main unit incorporates both an image signal processing circuit and a transmitting circuit. The image signal processing circuit converts an image signal to a video signal that represents an image that can be displayed by a monitor device. The transmitting circuit transmits the video signal by radio. A receiving device, which is provided outside the endoscope apparatus, receives video signal from the transmitting circuit and demodulates the video signal. Thus, this endoscope apparatus does not have a signal cable, which may extends from the endoscope main unit.
Endoscope apparatuses of this type are called “wireless endoscopes,” which can receive and transmit image data by radio. Having no data cables, the motion of their main unit is not so limited while the operator manipulates the endoscope main unit to observe the image of any object. In other words, the operability of the endoscope main unit is increased. As the operator moves the insertion section of the endoscope main unit is moved in a body cavity or a duct, the monitor device must display the image of the object in real time. To this end, the delay time between the generation of the image data and the display of the image data should be shortened as much as possible. In order to shorten delay time so much, the image data generated in the imaging unit of the endoscope apparatus is transmitted by radio in units of frames (or fields), each frame in frame time (or each field in field time), to the receiving unit of the receiving device. The receiving unit of the receiving device receives each frame within the frame time (or each field within the field time).
When the data is transmitted and received by radio, communication errors will be inevitably made due to the signal interference or reception failure induced by the environmental conditions.
Some methods that may be performed to prevent communication errors are known. One method is to transmit radio packets transmitted again and to add correction codes. This method can indeed lower the probability of communication errors, but cannot transmit all data in a normal sate within a specific time (one-frame time or one-field time) to shorten the delay time between the generation of the image data and the display of the image. Another method is to interpolate only packet data having an error in one frame, with the data corresponding to the frame received before in a normal state, or with the data of the packet being transmitted now.